In my experience, reticence to talk is mostly about fear of saying something stupid, which generally happens when you don't have anything to say but your trying to say something. Assigning people to talk for abitrary portions of the conversation might just cause you to say more stupid things. So, this is indeed a surprising result.
I sometimes think about something similar while watching sitcoms - the characters will often say/do mean things to each other for a laugh and because everyone on the show reacts as though what was said was okay/normal it seems to barely register to me how mean it actually was.
I think growing up with a critical sibling lead to me developing a self-critical voice that I carried around with me so even if externally people didn't react poorly to something "stupid" I said, internally I provided myself that negative feedback that reinforced my fears/beliefs. I think the self-critical voice was protective when it developed - it helped me avoid the more painful external feedback from my sibling, but it continued on long after that was useful.
When people let their guard down is when you get a glimpse into them.
Which I guess is why alcohol and similar substances have been used for centuries.
Being offensive certainly gives me a glimpse into the person but not in a good way.
I didn’t see the whole paper, but I wonder if the idea is really to be engaged in the conversation.